1. Field of the Invention
Aspects of the present invention relate to a secondary battery, and more particularly, to a secondary battery in which deformation of the insulation case can be prevented by forming the case thickly and in which unnecessary space between a cap assembly and the insulation case can be minimized by forming a recess that can receive at least a part of the cap assembly in the insulation case so as to maximize the capacity or minimize the size of the battery.
2. Description of the Related Art
Generally, the term “secondary battery” refers to a battery that can be recharged or discharged, as opposed to a disposable battery, which cannot be recharged. Secondary batteries have been used in many types of electronic devices including cellular phones, notebook computers, and camcorders. A lithium-ion battery has an operational voltage of 3.6V, which is three times higher than that of an Ni—Cd battery or an Ni—H battery and has a high energy density per unit weight. Therefore, lithium-ion batteries have been rapidly developed and are frequently used as power sources for electronic devices.
The lithium-ion battery uses lithium oxides as the cathode active material and a carbon material as the anode active material. Lithium-ion batteries are produced as various types, such as a cylindrical type, a rectangular type and a pouch type.
A rectangular secondary battery has an electrode assembly, a can that receives the electrode assembly and a cap assembly connected to the can. The electrode assembly includes a cathode, an anode, a separator interposed between the cathode and the anode and a cathode tab and anode tab extending from the cathode and the anode respectively. The can is a receptacle of a roughly rectangular shape, made of metal and is formed by a process such as deep drawing.
The can includes a closed end and an open end through which the electrode assembly is inserted in the fabrication of the battery. For convenience and clarity herein, the terms “bottom” and “lower” refer generally to a direction towards the closed end of the can and the terms “top” and “upper” refer generally to a direction away from the closed end of the can.
The cap assembly includes a cap plate connected to the upper part of the can, an electrode terminal installed through a terminal hole and having a gasket located on its outer face that insulates the electrode terminal from the cap plate, an insulation plate installed on the lower face of the cap plate, and a terminal plate installed on the lower face of the insulation plate and electrically contacting the electrode terminal.
The anode of the electrode assembly is electrically coupled to the electrode terminal through the anode tab and the terminal plate, and the cathode is electrically coupled to the cap plate through the cathode tab.
The rectangular secondary battery may further include an insulation case installed in the lower part of the terminal plate. The insulation case provides insulation between the electrode assembly and the cap assembly. The insulation case includes a plate that forms a base and a side wall that extends upwardly at the edge of the plate. The plate may include a slot through which the anode tab passes, a side groove formed on the side of the plate through which the cathode tab passes, a hole through which an electrolytic solution is injected, and a vent that allows gas generated inside the battery to escape.
However, the conventional insulation case has following problems. If, in an effort to maximize the size of the electrode assembly and therefore increase the capacity of the battery, the plate that makes up the base of the insulator case is formed too thin, it becomes more difficult to efficiently insert the insulation case inside the can because of deformation of the insulation case that can occur during injection molding of the insulation case. If the height of side wall is low, the insulation case may be easily deformed by external forces such as twisting, even after the insulation case is inserted in the can.
On the other hand, if the plate forming the base is made thick, it is possible to prevent the deformation of the insulation case, but the capacity of the battery is reduced because the size of the electrode assembly must be reduced to accommodate the thicker base.